My brother kept fish for years, never using any products at water change , all good no losses.
I myself use prime, i think its not worth the risk :sage: , especially if they change the amount of chlorine added to town supply.
Sorry for your loss , bummer you forgot :facepalm: , maybe smaller water changes are ok(still not worth the risk) without using, just not larger ones.
Does sound a bit strange that this happend though :-?